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Posted By Topic: Main Earth and Mains Neutral on same stud

Oct 26 2019 07:35

I've seen a few switchboards where the MEC and main incoming neutral conductor are on the same stud

These boards do not just have one bar for neutral and earth like some old ones do

They have an earth bar, MEN link and neutral bar

Both the main earth and incoming neutral are on the same stud on the neutral bar

Was this something that used to be ok? If I work on such a board at what point, if any, should I remedy this and move the MEC to the earth bar or should I just be leaving it as is as it?

Oct 26 2019 09:06

Under 1976 Regs, that was the required configuration.
You'll find older DBs & caravans set up the same way.
Under those rules, the connection had to be by nut & locknut

ESR 113 says it's OK to remain in service, ie the "no mandatory upgrade" principle that's almost universal in NZ law.

For a MSB, changing it doesn't make any difference to safety performance of the MEN system - which is what the N-E connection is about. But it does alter how we have to go about some kinds of testing.

For DBs & caravans, that config means the submain (supply lead) N & PEC are effectively in parallel; so the PEC will be carrying load current - which is not permitted for installations done to today's rules.
Also where there's multiple N-E connections, they ALL have to be found and opened when doing testing.
That's why we no longer use that configuration.


Nov 13 2019 13:09

To my interpretation ofAS/NZS 3019 4.3(f)

"Where there are separate earth and neutral bars, earthing conductors are connected to the
earth bar and neutral conductors are connected to the neutral bar"

it would fail a Section 4 periodic verification which is what some of the insurers seem to be requiring.

That opinion is worth exactly what you paid for it though

Nov 13 2019 13:25

No it wouldn’t fail anything. It was compliant when it was installed and remains compliant.

All periodic verifications must be carried out using the rules that applied when the installation or part installation was first livened.

The section of the rules that you have quoted refers to me work only..

Nov 13 2019 14:12

The section I have quoted refers to Verification by visual inspection and limited testing, specifically Inspection of switchboards.

I realise if it complied when it was built it complies now, but why does it reference "...separate earth and neutral bars..."? Is that intended to be for submains where the bars are electrically and physically seperate?

Nov 13 2019 16:42

I believe it's to distinguish between the separate bars we have now, and the older set-up with a single bar for both Ns & Es.

But you've highlighted a glitch, in that it needs to be amended to permit older MECs(earthing leads as it used to be) to remain on the N.

The revision of 3019 is under way now; so your timing is excellent